60 REPORT 1871. 



^200 have been received towards the cost of publication for the first year, 

 up to April 1872. 



There is good reason to believe that the expectations entertained of the 

 usefulness of these Reports will be fully realized by their continuance on the 

 present system, and that they wiU be found largely to conduce to the pro- 

 gress of the science wherever the English language is spoken. 



Report of the Committee for discussing Observations of Lunar Objects 

 suspected of Change. The Committee consists of the Rev. T. W. 

 Webb and Edward Crossley, Seci'etary. 



The Committee have much pleasure in presenting their first Eeport on the 

 above subject. Though much attention has been given of late years to a 

 large number of lunar objects, your Committee felt that they could not 

 accomplish their purpose better than by confining their Report to the discus- 

 sion of a limited and weU-observed portion of the lunar surface. No person 

 seeking to discover evidence of geologic change would be constantly travel- 

 ling over the whole surface of our globe, but would of necessity confine his 

 attention to a small area for a considerable period of time. This has been 

 the course adopted on the moon. Plato, a vast crater, containing 2700 

 square miles, in 51° N. lat. and 10° E. long., has presented a most interest- 

 ing and important variety of features, which we have endeavoured to photo- 

 graph, so to speak, with pen and pencil, with a view, if not at once to obtain 

 our iiltimate object, at least to lay out the groundwork for future observers. 



The Report has been carefully drawn up by Mr. "W. R. Birt on behalf of 

 the Committee. Time has only permitted the discussion of the observations 

 of the bright spots and craterlets seen on the floor of Plato ; whereas your 

 Committee consider that it is equally important that the observations of the 

 Humerous streaks, with the faults and other peculiar features noticed on the 

 floor and walls of this fine formation, should be likevdse discussed, in order 

 that something like a complete description of this object as observed at the 

 present time may be presented to the Association for the use of future sele- 

 nographers. 



Your Committee would therefore request that a further grant of £20 may 

 be placed at their disposal for this purpose during the ensuing year. 



Report on the Discussion of Observations of SjJOts on the Surface of the 

 Lunar Crater Plato. By W. R. Birt. 



In executing the task confided to me of discussing certain observations of 

 the spots on the lunar crater Plato, one of the first points which I deemed 

 it important to ascertain was the eifect which the intensity of the sun's 

 light as a function of his altitude might produce on the visibility of the spots. 

 The number of spots actually observed between April 18G9 and April 1871 

 inclusive, amounted to 37, the greater portion (21) having been discovered in 

 this interval. In order to become acquainted with phenomena possibly con- 

 nected with an increase of light on the floor of the crater, the observations 

 have been arranged under intervals of twelve hours, from suni-ise to sunset 

 on Plato, and a ledger formed for each interval, the number of which 

 is 31. Erom these ledgers the restdts in Table II. have been deduced, 

 viz. the mean number of spots visible during each interval, and the actual 

 number of spots observed during each interval. For illustrating the results 



